There are a lot of different reasons for using a conformal coating material or Parylene to protect a printed circuit board (PCB).

These reasons can include:

Barrier protection

High insulation protection

High moisture and humidity protection

Chemical and temperature resistance

Ruggedising

Improve dielectric properties

There are a lot of different reasons for using a conformal coating material to protect a circuit board including barrier protection, increased insulation resistance, chemical protection and increased dielectric properties

Barrier protection

A conformal coating can create a barrier against attack during the lifetime of the circuit board.

The coating material can prevent various types of particulate contamination reaching the surface of the circuit board, which can lead to problems such as corrosion.

High insulation protection

Conformal coatings can provide a high degree of insulation protection for the circuit board during its lifetime when applied as a protective lacquer.

The circuit board normally starts with a high level of insulation when it is first manufacture as it is normally clean.

However, with time in the field and its natural environment the circuit can degrade in different ways.

The conformal coating can slow this degradation down.

High moisture and humidity protection

Printed circuit boards can be vulnerable to moisture and humidity whilst in the field during its lifetime.

Most conformal coatings are highly resistant to moisture and humidity and this can lead to a reduction in leakage currents, cross talk, electrochemical migration, dendrite growth and arcing across the circuit board.

Chemical and temperature resistance

Some conformal coatings can be highly resistant to many types of solvents, chemical attack and be heat resistant.

Normally, a circuit board exposed to chemically aggressive environment would be attacked but the conformal coating can slow down the effects or even prevent them.

Ruggedising

Conformal coating can prevent damage from rough handling, installation and reduction of mechanical and thermal stress.

Improved dielectric properties

Just as the conformal coating can protect the circuit from moisture it can also help to increase the dielectric strength on the circuit board between components and lead interconnects.

This enables the design of the PCB to be more compact and small.

Need to find out more?

For further information on using conformal coatings then contact us directly.

Coating LEDs to protect them is big business. The volume of manufactured LEDs globally is growing at an exponential rate and there is no end in sight.

However, the challenges to protect them are not small especially in an outdoor environment.

The LED circuits are placed in exposed areas and subjected to the full force of the elements. Then they are expected to survive for long periods of time.

Further, the protection placed on the circuits must not affect the light output of the LED (the lux) or cause heating problems due to thermal demands.

Finally, due to the low cost of the LED products in the first place then the protective method of coating and application has also to be extremely low in price.

Due to the low cost of the LED products in the first place then the protective method of coating and application has also to be extremely low in price.

This final point can be the most challenging. After all protecting the LEDs is relatively easy with certain coating materials. Coating the unit for the right price is the key challenge.

This price challenge is due in most cases to the insulative properties of the majority of coatings applied. Nearly all of the traditional coating methods require components like connectors not to be coated since they would ruin the electronic properties of that component.

This leads either to masking of components in process or selective processing that leads to increased costs in prodution.

To provide a high level of protection whilst being low cost is not a trivial task for a coating. Processes like Parylene, conformal coatings, encapsulates and potting compounds continuously find it difficult to meet all of these criteria and customers are continuously compromised.

So, is there an alternative protective coating for LEDs besides Parylene, conformal coatings and encapsulates?

Nexus has been examining a new, novel technique that may be able to meet all of the environmental demands for LEDs and actually be cost-effective.

The final coating built up is much thinner than the other traditional coatings including Parylene. However, its protective performance has been found to be superior to them all in most categories of testing so far.

Further, the really exciting part about this technology is the cost of processing.

Since the coating is extremely thin then it has been found that no masking is required.

This is because when components like connectors are joined together then the ultrathin coating does not prevent electrical connection. Even better, the physical protection is not compromised.

This means that the cost of process is purely the cost of application of the material and nothing else.

Since the process is relatively low cost then this does offer a very interesting alternative to the traditional coating materials.

Sounds complex?

Actually, although the technology and chemistry can be a little complex the process itself is fairly simple.

Once the process is set up in the machine the operator just loads, switches the machine on and unloads on completion.

This is a far cry from the sophisticated processes of robotic selective coating or the challenges of Parylene. Further, the process is actually very stable and in reality is tried and test in other industries.

So what does a hybrid ALD / CVD film look like?

The film is built up of alternating layers of ALD and CVD thin coating layers. The ALD is a ceramic-based material providing the insulating properties and the CVD film provides the barrier protection.

Once the required film thickness is achieved then a final hydrophobic layer is applied that combines with the ALD and CVD layers to provide a highly effective barrier.

The film is built up of alternating layers of ALD and CVD thin coating layers. The ALD is a ceramic-based material and the CVD film is an organic layer.

So how well did the hybrid coating perform in protecting LEDs?

Nexus actually worked with live LED circuits from a customer.

The customer LED product was for outdoor application. For testing the customer used their own in-house test methods to prove the technology.

The LED circuit was exposed to customer tests for resistance against salt, moisture and temperature.

The test methods included:

Initial test submerged in DI water dip for 12 hours

Second test submerged in 25% concentration saltwater dip for 17 hours

Third test 2 x 6 hour cycles in water ramped from room temperature to 70°C

After each test the boards were tested for failure or problems.

The LED circuit passed on all tests. All results achieved were completed with no masking of components and zero light loss in LED opacity.

The electrical connections were found to be excellent and the coating did not effect the integrity of the connectors.

So what about the cost of process?

Since the process is masking and de-masking free then the cost per unit is incredibly low and superior to nearly all the traditional methods of coating protection.

Further, the protective properties of the hybrid coating in nearly all cases is superior to the conventional methods.

So, you get a lower cost coating with a higher technical performance.

So, just how good is the hybrid coating as a protective material for electronics?

Generally, with protective coatings for electronics then Parylene is considered the gold standard in most cases.

So, we compared Parylene with the hybrid ALD / CVD material.

Property

Parylene

ALD/CVD Coating

Hardness

Soft

Hard

Wear resistance/Handling Ease

Poor

Excellent

Water Vapor Transmission Rate

Good

Excellent

Temperature Resistance (extended time)

100°C

350°C

Color

Gray/white

Clear

Adhesion to various materials

Poor

Excellent

Scalable to large production

Poor

Excellent

Process Time

8 – 12 hrs

8 – 12 hrs

Hydrophobicity

Good

Good – Excellent

Cost

High

Low – Med

What we also identified for the material were some key properties for LEDs.

The Water Vapor Transmission Rate (WVTR) is superior to Parylene so the coating is far more waterproof for the LEDs

Coating adhesion is superior as it covalently bonds to the substrate. So, the lifetime of the material will be better on the circuit.

The hybrid coating is UV stable whereas Parylene in general is not. This is an important criteria for coatings exposed outside on LEDs

The coating stayed 100% transparent during testing (no loss of lux). That again is important for LEDs.

The coating thickness of the hybrid material is x10 LESS than the Parylene. This aids light transmission and electric connectivity

So, in reality the hybrid ALD / CVD material could just be what the LED industry is looking for in protecting their circuits. Nexus will let you know how the material performs on other types of circuits shortly.

Need to find out more?

If further information on these topics and the key question you can go to our free eBook by clicking conformal coating design now.

If you are new to Nexus and our work on conformal coatings then a good place to go is our Start Here page.

Dr Lee Hitchens, Author of Nexus

Dr Lee Hitchens, Author of Nexus

Dr Lee Hitchens is the author of the Nexus conformal coating website and eBook.

Send me an email at lhitchens@nexus3c.com and let me know what you think?

Water repelling (hydrophobic) Properties – An ultra-thin coating is normally hydrophobic. This is because it is normally a fluoropolymer technology. The coating does not allow the water to wet on the on the surface of the coating. It modifies the surface and changes its dyne energy. A typical conformal coating like an acrylic or polyurethane is not water repellent and water wets the surface.

Ultra-thin –Typical coating thickness is 1-2um for a coating (depending on application) compared to the acrylic, urethane and silicone conformal coatings that are applied at >25um.

No masking of connectors required – The circuit board can be completely submerged in the coating liquid with no masking applied. Due to the extremely thin coating applied (<1-2um), the components can be connected together and the electrical connection is easily made. This would not be possible for a standard conformal coating. So, costs of processing are extremely low.

Simple application process – The ultra-thin coating can be applied by dip, brush or spray. But, the simplest method is dipping. Since there is no masking then the dip process is simple and is an extremely cost effective application method.

Fast drying – Since the coating is ultra-thin and the solvents normally used are fast drying then the fluoropolymer coating dries extremely quickly. The coating can be dry in seconds and ready for use in a few minutes.

Need to find out more?

For further information on the ultra-thin, nano- coatings then contact us directly.